The objective of the proposed research is to study the central nervous control of accommodation, pupil size and choroidal blood flow. The nucleus of Edinger-Westphal (EW), via its projection to the ciliary ganglion, is involved in the mediation of all three of these clinically important visual functions. EW in birds is much more clearly delineated in its cytoarchitecture than in mammals, and two morphologically distinct subpopulations of neurons (i.e. choroid and ciliary) have been described in the avian ciliary ganglion. Our previous studies of the central control of the pupillary light reflex and choroidal blood flow have identified two bisynaptic retinofugal pathways projecting to different subdivisions of EW. A third subdivision of EW may be involved in the control of accommodation. The major goals of the present proposed studies are to determine: (1) the central pathways controlling accommodation, (2) the subdivision of EW to which each of these central pathways projects, (3) the differential projection of the three subdivisions of EW on the two cell types in the ciliary ganglion, (4) other afferent and efferent connections of the retinorecipient nuclei in the pupillary reflex and choroidal pathways, and (5) the morphology and regional distribution of the retinal ganglion cells giving rise to each of the pathways that input to the different subdivisions of EW. Anatomical methods, including microstimulation in conjunction with discrete lesions and conventional pathway tracing techniques (i.e., autoradiography, HRP and immunohistochemistry), will be used. In order to help establish the visual function(s) of specific pathways, both pupillometry and retinoscopy will be used to measure changes in pupil size and accommodative state of the eye during microstimulation of selected neuronal structures. These proposed studies will help elucidate the anatomical substrates mediating accommodation, the pupillary response and choroidal blood flow. This anatomical knowledge may provide critically needed experimental models for the future investigation of both developmental problems in accommodation (i.e., myopia) and the reported role of choroidal blood supply disorders in some retinal dystrophies.